36. Out of the statements mentioned below

    A. L-threonine and L-allo-threonine interact identically with plane polarized light.
    B. van der Waals’ interactions are always attractive.
    C. Poly (pro) ll-helix is not stabilized by intermolecular hydrogen bonds.
    D. The folding of a protein is associated with an overall positive change in free energy and negative change in entropy.
    E. Lysine acetylation on histone is associated with loosening of the histone complex from DNA.

    Which of the following combinations is CORRECT?
    (1) A and C
    (2) B and D
    (3) C and E
    (4) D and E

Understanding Protein Folding, van der Waals Interactions, and Histone Acetylation

Biomolecular interactions play a vital role in determining protein structure, stability, and function. Concepts like van der Waals forces, polyproline helices, and histone modifications are fundamental for CSIR NET Life Science aspirants.

Correct Answer:

The correct option is (3) C and E.

Explanation:

(A) L-Threonine and L-Allo-Threonine Interact Identically with Plane Polarized Light ❌

• L-threonine and L-allo-threonine are diastereomers, meaning they have different spatial arrangements.
• Since diastereomers have different optical activities, they do not interact identically with plane-polarized light.
• Therefore, this statement is false.

(B) van der Waals’ Interactions Are Always Attractive ❌

• van der Waals interactions have both attractive and repulsive components.
• Attractive forces occur due to London dispersion interactions.
• Repulsive forces arise when electron clouds of atoms overlap.
• Since van der Waals forces are not always attractive, this statement is false.

(C) Poly (Pro) II-Helix Is Not Stabilized by Intermolecular Hydrogen Bonds ✅

• The polyproline II (PPII) helix is a unique secondary structure seen in collagen and unfolded proteins.
• It lacks hydrogen bonds for stabilization, unlike α-helices and β-sheets.
• Instead, it is stabilized by steric constraints and backbone rigidity.
• Since this statement is true, it is part of the correct answer.

(D) The Folding of a Protein Is Associated with an Overall Positive Change in Free Energy and Negative Change in Entropy ❌

• Protein folding leads to a negative change in free energy (ΔG < 0), making it a spontaneous process.
• The entropy of the protein decreases as it folds, but the overall system entropy increases due to the release of ordered water molecules.
• Since protein folding is associated with a negative ΔG, this statement is false.

(E) Lysine Acetylation on Histone Is Associated with Loosening of the Histone Complex from DNA ✅

• Histones have positively charged lysine residues, which tightly bind negatively charged DNA.
• Acetylation neutralizes the positive charge, reducing histone-DNA interaction.
• This leads to chromatin relaxation, making DNA more accessible for transcription.
• Since this statement is true, it is part of the correct answer.

Thus, the correct answer is (3) C and E.

Nearby Topics for Better Understanding

1. van der Waals Interactions in Protein Folding

• Essential for protein stabilization.
• Includes London dispersion forces, dipole-dipole, and induced dipole interactions.

2. Types of Protein Secondary Structures

3. Role of Histone Acetylation in Gene Expression

• Histone acetylation → Chromatin loosening → Gene activation.
• Histone deacetylation → Chromatin tightening → Gene repression.

4. Importance of Protein Folding in Disease

• Misfolded proteins contribute to Alzheimer’s, Parkinson’s, and prion diseases.
• Correct folding is essential for enzyme function.

Conclusion

Protein folding, secondary structures, and histone modifications are crucial in molecular biology. Mastering these concepts will enhance understanding for CSIR NET Life Science aspirants.